Although no formal definition exists for what constitutes a rapidly progressive dementia (RPD), generally we use the term when dementia occurs in <1–2 years from illness onset, but more commonly over weeks to months. Prion diseases are the prototypical causes of RPD, but reversible causes of RPD might mimic prion disease and should always be considered in a differential diagnosis. We report the case of a 65-year-old male with progressive dementia and typical neurologic symptoms, myoclonic jerks, and magnetic resonance imaging findings of Creutzfeldt–Jakob disease (CJD). This case highlights the need for a high index of suspicion to diagnose CJD.